Voltage and Reactive Power Support for Grid Connected Solar Power Plants

1. T&D India October 2016
Technical Insight
34
raditionally voltage support
in the grid is provided by
synchronous generators.
There is increased penetration of
solar plants in the grid but when it
comes to supporting reactive power
needs of the grid, there is not much
clarity as to how the solar plants
need to contribute to voltage support
by supplying reactive power needed
for the purpose.
There are no clear guidelines or
norms in this regard resulting in
confusion and halfhearted efforts.
There is great disconnect between
utilities and solar plant operators
on the issue. There is no uniform
policy across states. Most solar plant
developers are unaware of the issue.
Many come to know of it while
seeking to get approval for grid
connections. Sometimes, they realize
the existence of the issue when
discoms (distribution companies)
start billing them for drawl of
reactive power from the grid. There
is also vagueness about the type of
reactive power support needed of a
grid-connected solar plant.
Some utilities ask for dynamic
reactive power support while others
are silent on the type of requirement.
Utilities need to specify the reactive
power source dynamic range and
also the complete range. The cost of
these systems is almost invariably not
factored in the budget by developers. If
afullydynamicsystemistobeinstalled
the additional investment makes the
plants economically unviable. If the
guidelines are clearly defined and
knowntothesolardevelopersatdesign
stage a combination of measures can
help in achieving the objective at a
judicious and a workable cost. The
measures are:
• Proper sizing of grid inverter
• Defining and formulating
operating parameters of grid
inverter
• Designing a hybrid solution
consisting of dynamic active
component and passive fixed or
auto controlled component
It has been observed that for
installing an additional reactive
power support for an existing
solar generation facility to avoid
reactive power billing by discom the
investment needed pays back for
itself in 12-24 months depending
uponthetariffstructureandtherange
of reactive power source over which
the dynamic operation is built into
the system. Grid inverters can also
be adequately sized and configured
to both supply and absorb some
amount of reactive power as needed.
This will proportionately reduce cost
of additional reactive power source
required for the solar plant.
Grid-connected solar plants
present unique issues of grid
stability and additional reactive
power burden on the grid. To have
a smooth and consistent evacuation
of power from a solar plant a stable
grid is essential. Utilities have been
insisting on installation of dynamic
reactive power system at solar
generating plants to maintain grid
stability.
Voltage and reactive
power support
Baldev Raj Narang
T
Grid-connected Solar Power Plants in India

2. Technical Insight
October 201635T&D India 35
The main purpose of the dynamic
compensation system is to ensure
that there is no drawl of reactive
power from the grid and all
additional reactive power burden as
a result of export of power by solar
plants is shared by these plants on
real time basis.
Power utilities face many
challenges related to reactive power.
There are strict regulations by
some utilities like Karnataka State
Electricity Board for grid-connected
solar plants. Some other discoms,
where no such regulations exist, are
charging solar plants for reactive
energy units drawn from the grid as
a result of additional reactive power
burden on the system where solar
plants are exporting power to grid.
The transmitted load often varies
considerably in the grid from
one hour to another; the reactive
power balance varies as well. The
result can be unacceptable voltage
amplitude variations, a voltage dip,
or even a voltage collapse. Voltage
unbalance, poor power factor and
flicker are some of the other issues
confronted by the grid.
Dynamic reactive power control
with STATCOM can resolve all
the above issues by improving
the power factor or compensating
for the voltage instability. The
normal reactive power control by
generators or capacitor banks alone
is too slow for the sudden load
changes. STATCOM also has the
capabilities of harmonic mitigation
and unbalance control. It is a
voltage source converter device and
acts as a step less variable source of
reactive power. It also has distinct
advantages over standard reactive
power compensation systems and
is ideal for demanding applications
such as those prevailing during
highly fluctuating grid conditions.
In order to optimize the cost a
hybrid solutions involving a passive
unit consisting of fixed Reactive
Compensation and an Active unit
consisting of fully controllable
IGBT based power electronic device
called STATCOM can be employed.
STATCOM is capable of providing
both capacitive and inductive
power. This feature is used to retain
step less control over the entire
range in a hybrid installation n
Baldev Raj Narang is an Electrical
Engineering Graduate from Delhi
College of Engineering, University
of Delhi and is currently CEO of
Pune-based Clariant Power System
Ltd, a company which in association
with FRAKO Germanyis engaged in
providing solutions in reactive power
systems and power quality management
to Indian and overseas customers in
diverse fields. Narang has previously
worked for Indian Oil Corporation and
Century Enka Ltd among others. He
can be reached at baldevrajnarang@
clariantindidia.co.in or on
+91-77-19-99-68-68.